This invention relates to an occlusion device for the closure of physical anomalies like vascular or septal apertures, such as patent ductus arteriosus, patent foramen ovale, atrial septal defects, or ventricular septal defects. More specifically, this invention relates to a method of forming a polyvinyl alcohol (PVA) foam treated with heparin for use in occlusion devices. The resulting PVA foam structure minimizes blood clotting.
Normally, permanently repairing certain cardiac defects in adults and children requires open heart surgery, a risky, expensive, and painful procedure. To avoid the risks and discomfort associated with open heart surgery, modern occlusion devices have been developed are that small, implantable devices capable of being delivered to the heart through a catheter. Rather than surgery, a catheter inserted into a major blood vessel allows an occlusion device to be deployed by moving the device through the catheter. One method of inserting an occlusion device begins by using a guide catheter introduced through the femoral vein and lower vena cava and placed in the right ventricle of the heart. After passing through the defect in the atrial septum, the distal portion of the implant is forced out of the catheter and unfolded in the left atrium, much like unfolding an umbrella. The unfolded portion is drawn back against the septum due to the pre-tensioning of the fixation devices. Then, the proximal parts of the implant are likewise pushed out of the catheter and independently unfolded in the right atrium. The insertion forceps used to guide the occlusion device through the catheter are then separated from the center piece.
This procedure is performed in a cardiac cathlab and avoids the risks and pain associated with open heart surgery. These modem occlusion devices can repair patent foramen ovale, patent ductus arteriosis, atrial septal defects, ventricular septal defects, and other cardiac and non-cardiac apertures. One such device is that disclosed in PCT application PCT/US98/15961, entitled Occlusion Device for the Closure of a Physical Anomaly Such as a Vascular Aperture or an Aperture in a Septum, filed on Jul. 31, 1998 by Bernhard Schneidt, now issued U.S. Pat. No. 6,174,322. This patent discloses a non-thrombogenic occlusion device that is insertable into an anomaly via a catheter. In addition, a similar device filed as German Appln. 297 14 242.9 on Aug. 8, 1997, discloses an occlusion device which can be inserted via a catheter. Another devices is that disclosed in U.S. Pat. No. 6,206,907, entitled Occlusion Device with Stranded Wire Support Arms, filed on May 7, 1999, invented by Joseph A. Marino, Michael P. Corcoran, and Peter M. Buonomo.
There are several types of these new occlusion devices capable of being inserted via a catheter, including button devices, collapsible umbrella-like structures, and plug-like devices. One major draw back is that the intent of some of these occlusion devices is to stimulate thrombosis, or a blood clot. This stimulation of a blood clot (thrombosis) on the device creates one of the biggest concerns in closing a defect. Such a clot may lead to a stroke if the clot should pass from the right atrium to the left atrium, pass through to the left ventricle, through the aorta, and to the brain.
Thus, there is a significant need in the art for an occlusion device that will occlude septal defects and will minimize thrombosis occurring at the device.
The present invention alleviates concerns with blood clots forming around an occlusion device used to close a physical anomaly, such as a patent foramen ovale. The present invention is an occlusion device for closure of a physical anomaly. The occlusion device is comprised of a center section, to which is attached upper and lower elastic shape memory fixation devices. Attached to the fixation devices are sheets (e.g. polyvinyl foam sheets) which serve to occlude the anomaly. The polyvinyl alcohol foam sheets are treated with heparin. Heparin minimizes or eliminates thrombosis formation and bonds well to polyvinyl alcohol foam. Because of the heparin, the chances of a blood clot forming at the occlusion device are reduced and almost eliminated.
To create the non-thrombogenic PVA foam structure, the PVA foam structure is treated with a PVA heparin gel. The PVA heparin gel comprises a PVA in a gel form having heparin bonded to the PVA. By soaking the PVA foam structure in the mixture of PVA and heparin, the PVA molecules of the foam structure may bond to the PVA molecules in the PVA heparin mixture. The PVA molecules in the mixture which bond with the PVA molecules in the foam also comprise heparin. As a result, the PVA foam structure has long lasting non-thrombogenic properties that do not dissipate or wash off.
A first PVA sheet is attached to the upper fixation devices and a second PVA sheet is attached to the lower fixation device. The shape of the foam sheets can be a square, a circle, or any other such suitable shape. The sheet on the upper fixation device may be oriented asymmetrically from the sheet on the lower fixation device. This is advantageous in that a wider variety of anomalies can be closed using such an arrangement, including anomalies of different sizes and shapes.
Once attached to the center section, the fixation devices and the attached foam sheets are collapsible so that the entire occlusion device can be moved through a catheter. The fixation devices hold the occlusion device in place once it is inserted into an aperture. To prevent any damage to surrounding tissue, the fixation devices are fitted with atraumatic tips. In addition, the fixation devices have a shape memory, which allows the fixation devices to return to their original shape, or xe2x80x9crememberxe2x80x9d their shape even after being bent or deformed for passage through a catheter. In setting the shape, the deformation caused by passage through a catheter is taken into account.